This invention concerns star polymers having acrylic arms and crosslinked polysiloxane cores formed by condensation reactions of one or more substituent alkoxysilyl functional groups attached to pendant ester groups of the arms.
A. Aoki et al., U.S. Pat. No. 4,304,881 (1981), prepared styrene/butadiene "living" polymers by anionic polymerization and then coupled them by reaction with silicon tetrachloride to produce a 4-arm star polymer having a silicon atom as a core as shown in Example 4.
H. T. Verkouw, U.S. Pat. No. 4,185,042 (1980), prepared a polybutadiene "living" polymer by anionic polymerization and then prepared a silicon-containing star with up to 3.1 arms by reacting the "living" polymer with gamma-glycidoxypropyltrimethoxysilane.
O. W. Webster, U.S. Pat. Nos. 4,417,034 (Nov. 22, 1983) and 4,508,880 (Apr. 2, 1985), and W. B. Farnham and D. Y. Sogah, U.S. Pat. Nos. 4,414,372 (Nov. 8, 1983) and 4,524,196 (June 18, 1985) showed that acrylic star polymers can be prepared via group transfer polymerization by coupling "living" polymer with a capping agent having more than one reactive site or by initiating polymerization with an initiator which can initiate more than one polymer chain. Initiators that could produce acrylic star polymers with up to 4 arms were demonstrated.
H. J. Spinelli, in U.S. Pat. Nos., 4,659,782 and 4,659,783 issued Apr. 21, 1987, teaches the preparation of acrylic star polymers with crosslinked acrylic cores and at least 5 arms, optionally having functional groups in the cores and/or the arms. Preferably GTP techniques are used to make the polymers.
R. P. Zelinski et al. in U.S. Pat. No. 3,244,664 describe a three-step process for coupling polymer chains involving (1) the preparation of an addition polymer having one or two terminal alkali metal atoms on the polymer main chain, or backbone, then (2) reacting the alkali metal atoms with certain silicic compounds to give a polymer product containing reactive silicon-containing terminal groups, and in which reaction some coupling of molecules can occur, and then (3) further treatment of the product which can provide additional coupling. The polymers can be telechelic (a reactive group on each end of the molecule) or semi-telechelic (a reactive silicic group on only one end). Because of the nature of the process only one alkali metal atom, if any, and therefore only one silicon atom or one silicic group, can be attached directly to any one end of the polymer molecule. The single silicon group per end and the attachment to the end of the polymer backbone limits the nature and extent of the subsequent coupling or crosslinking possible among the molecules. Furthermore, the polymerization process of the reference is subject to termination reactions which result in some polymer chains being unable to react with the silicon group and consequently unable to couple or crosslink at all.
An object of this invention is an improved hybrid star polymer comprised of a crosslinked polysiloxane core with arms of linear acrylate and/or methacrylate polymers.